Modulation



May 21, 1935.

H. O. ROOSENSTEIN MODULATION Filed May 5, 1952 2 Sheets-Sheet l INVENTORHANS o- ROOSENSTEIN BY rww ATTORNEY y 1935- H. o. ROOSENSTEIN 2,001,891

MODULATION Filed May 5, 1932 2 SheetsSheet 2 INVENTOR HANS 0.ROOSENSTEIN ATTORNEY Patented May 21, 1 935 UNITED. STATES- Hans OttoRoosenstein, Berlin, Germany, assignor to Telefunken Gesellschaft fiirDrahtlose Telegraphie, m. b. 11., Berlin, Germany, a corporation ofGermany Application May 5, 1932, Serial No. 609,422

i In Germany May 21, 1931 sclaims. (c ne-1'11) .This invention relatesto a method of and meansqfor producing and utilizing frequency modulated.waves.

"In order to modulate the frequency of a valve 5- transmitter as knownin the prior art one of the frequency governing elements may be variedat the rhythm of the modulation. This element most preferably consists,in the case of a valve generator, of part of the capacity of theoscillalfll tion circuit. It is comparatively easy to design I.condenser of this kind'in such a. way that, when driven. by a motor, itwill occasion a periodic alteration of the transmission'frequency at therate orrhythm of the rotations of said motor. to However, arrangementsof. this sort fail to work when it is desired to change the transmissionfrequency at a veryhigh rate of speed inasmuch as the speed of rotationof such a condensercan not be: pushed very far. Also frequencymodulation case a condenser must. be used whose capacity, for instance,by varying the inter plate distance is to be varied in an inertialessmanner'at the rate and rhythm ofvoice frequencies. For this 25: purposecould beemployed, for instance, a two plate condenser; One of theseplates consists of a. steel diaphragm which is attracted by the magneticfield of an iron containing (iron cored) coil through which currents ofvoice frequency flow. Thedifiiculty inherent in the construction of sucha device resides in the low capacity variatime thatis attainable, and inthe mechanical inertia of the system for response to the highest voicefrequencies is hard to insine;

The object. of the present invention is to provideanarrangementtoovercome the above difficulties.

In describing the present invention reference will be made to thedrawings, in which:

Figure 1 illustrates diagrammatically one manner in which frequencymodulated waves may be produced and an arrangement for producing thesame;

Figure 2 shows another arrangement for producing frequency modulatedwaves;

Figures 3, 5 and 6 show modifications of the arrangement of Figure 1;while,

Figure 4 shows a modification of the arrangement of Figure 2. 50According to the present invention, therefore, the wave generator oroscillator whose frequency is to be modulatd is so designed that slightalterations of a resistance will result in relatively large variationsin the frequency. This scheme is feasible, for instance, in a standardvalve genof a transmitter by voice is difiicult because in this eratorif the oscillation circuit which is to gov- .ern the frequency is givenparticularly high damping. It is also feasible to use generators whosefrequency is a direct or linear function of the resistance In thisconnection, referring to Fig. 1, suppose G is an oscillatinggaseous-comduction lamp whose time of vibration is of. the order of magnitude ofthe product T=R.C. An-' other generator whose frequency is governed inthe main by a time constant is the multivibr ator system Abraham andBloch or elsethe multivibrator suggested by Van der P01 and Roosenstein;Such a multivibrator has been shown in Van der Pol, PatentNo.'1,744,935. I

In the generator arrangement shown in Fig. 2 oscillations are developedin the thermionic tube and circuits connected between the anode andinner grid and outer grid. The oscillation producing circuits includethe condenser C, the resistance R, the battery B, etc., as shown. Thefrequency of the oscillations generated is governed by the size of thegrid blocking condenser C and the leak resistance R. If in generators ofthis nature the frequency-governing resistance is replaced by 'anamplifier tube, as shown, for exam ple, in Fig. 3, where the resistanceR'of Fig. l is replaced by the impedance of tube V or bridged by anamplifier tube as shown in Figure 4, where the resistance R of Fig. 2 isbridged by the impedance of tube V, and if the grid of this amplifiertube is energized by voice frequencies, then the frequency of thegenerator will be modulated approximately proportionallyto thevariations of the tube resistance. Another merit of this arrangement isthat the ensuing amplitudemodulation is but slight. Generators of thekind-here mentioned are mostly not in a position to produce very shortwaves. However the wave which is generated contains a large number ofharmonics or overtones for which reason it is possible with this cicui'tarrangement to obtain frequency modulated short waves. For example, anarrangement as shown in Fig. 5 may be utilized. In this arrangement, theoscillation generator and frequency modulator may be as disclosed inFig. 3. Here, however, a harmonic or overtone of the frequency modulatedoscillations is separated out by a filter circuit 2 and supplied to apower amplifier PA, in which the amplitude of the overtone may be raisedthe desired amount. The amplified frequency modulated overtone may beutilized in any manner. For example, the power amplifier may feed theamplified frequency modue lated overtone to an aerial system forradiation as shown. To be sure, the circumstance that the frequency ofthe generators is easily variable by small resistances may turn out tobe a disadvantage seeing that slight variations in thetube data, such asfilament potential and plate potential are able to alter the frequencyto a comparatively large extent. In order that these changes maynot'become so noticeable the wave of the generator is suitably modulatedupon a generator of extremely constant frequency, such as a crystalcontrolled generator valve, with one of the two side-bands being usedfor the transmission. 1 An'arrangement as briefly described above hasbeen illustrated in Figure 6. In thearrangement of Figure 6 anoscillation generator and frequency modulator as disclosed in Figure 3is utilized to supply an overtone by way of filter 2 to a modulatorstage 4. The filter 2 may be tuned to the fundamental or an overtone ofthe oscillations generated and frequency modulated in the precedingcircuit. The filter 2 supplies the fundamental or overtone to themodulator 4, which is also coupled to an oscillation generator 3 whichmay be of any type but is preferably of the crystal controlled type asshown. The output cir- ,cuit of tube itherefore contains complexcurrents principally consisting'of the frequency of the quartzcontrolled oscillator 3 and the two side bands which are spaced adefinite distance aparton eachside of th frequency oi the quartz crystaloscillator 3, the distance apart being equal to the widthof transmissionof the frequency of filter 2. In order to insure that, of these complexcurrents in the output circuit of stage 4, only one of the two frequencymodulated side bands may be sent out, the stage 4 is followed by bandpass filters 5 and 6. The band pass filter B supplies the selected sideband to a load circuit by way of a power amplifier. PA. The frequencymodulated waves may be supplied from the gen erator and modulator to anywork circuit as shown.

I claim: 7 v

1. Means for producing high frequency oscillations and for modulatingthefrequency thereof at signal frequency comprising, a thermionic tubehaving an anode and a cathode, an inner grid and an outer grid, a sourceof potential and a resistance connected between said inner grid and saidcathode, a resistance connected between said outer grid and saidcathode, a capacity connected between said inner grid and said outergrid, a connection between a point on said source of potential and theanode of said tube, means for connecting autilization circuit betweenthe anode and cathode of said tube, a second thermionic tube havingelectrodes including, an

anode, a cathode and a control grid, a connection between the anode ofsaid last named tube and the outer grid of said first named tube, aconnection between the cathode of said second named tube and the cathodeof said first named tube, and means for applying modulating potentialsbetween the control grid and cathodeof said second named tube.

2. Means for producing undulatory electrical energy comprising,oscillation generating means including, a thermionic tube having anode,cathode, and a plurality of auxiliary electrodes, circuits forv applyingpositive potentials between said anode and cathode and between one ofsaid auxiliary electrodes and said cathode, frequency determining'circuits connected between the auxiliary electrodes and thecathode of said tube, one of said circuits including a frequencydetermining capacity and a resistance in series, and means for"modulating the frequency of the oscillations produced linearly at.signal frequency-including, a second resistance in parallel with saidseries resistance and capacity, a second thermionic tube having anode,cathode .and control grid, a circuit connecting the anode to cathodeimpedance of said second thermionic :tube in parallel with said secondresistance, and circuits for applying modulating potentials between thecontrol grid and cathode of said last-namedtube. v

3. Means for producinghigh frequency oscillations comprising, athermionic tube having an anode and a cathode, an inner grid andan-outer grid, circuits for applying positive potential between theanode and cathode of said tube and between one of said grids and thecathode of said tube, said circuits including a resistance connectedbetween one of said grids and said cathode, and a resistance connectedbetween the other of said grids and said cathode, a capacity betweensaid inner grid and said. outer grid, means for connecting a utilizationcircuit between the anode and cathode of said tube, whereby oscillationsare produced in said tube and appear in said utilization circuit, andmeans for modulating the frequencyrof the oscillations produced linearlyat signal frequency comprising, a second thermionic tube having ananode, a cathode, and a control grid, va connection between the anode ofsaid last-named tube and a point on one of said resistances, aconnection between the cathode of said last-named tube and a secondpoint on said one of said resistances spaced with respect to saidfirst-named point, and a circuit for applying modulating potentialsbetween the control grid

